Inclusion Criteria:

- Men and women ≥ 18 years of age

- Documented diagnosis of myelodysplastic syndromes (MDS) or non-proliferative chronic
myelomonocytic leukemia (CMML), White blood cells (WBC) ≤ 13,000 /mm3, World Health
Organization (WHO)) that meets International Prognostic Scoring System (IPSS)
criteria for low or intermediate-1 risk disease

- Anemia, Hemoglobin (Hgb) ≤ 9.0 g/dL or ≥ 2 units of Red Blood Cells (RBCs) within 84
days

- No response or loss of response to Erythropoiesis-Stimulating Agents (ESAs) or
erythropoetin (EPO) > 500 mU/ml

- Eastern Cooperative Group (ECOG) score ≤2.

- Creatinine < 1.5 X Upper Limit of the Normal (ULN)

- Total bilirubin ≤3.0 mg/dL

- Aspartate aminotransferase (AST)/Serum glutamic oxaloacetic transaminase (SGOT) &
Alanine Aminotransferase (ALT)/Serum Glutamic Pyruvic (SGPT) ≤3.0 x Upper Limit of
Norma (ULN)

- Free of metastatic malignancy (other than MDS) for ≥2 years

- Highly effective methods of birth control for females & males

Exclusion Criteria:

- Chromosome 5q deletion

- Pregnant or breast feeding women and males who do not agree to use condom during the
sexual contact with females of childbearing potential.

- Major surgery within 30 days

- Incomplete recovery or incomplete healing of wounds from previous surgery

- Heart failure ≥3 (New York Heart Association(NYHA))

- Thromboembolic or myocardial infarction event within 6 months

- Concurrent anti-cancer cytotoxic chemotherapy

- History of severe allergic or anaphylactic reaction or hypersensitivity to
recombinant protein

- Known positive for Human Immunovirus (HIV) or infectious Hepatitis type C or active
infectious Hepatitis type B.

- Clinically significant anemia unrelated to MDS

- Thrombocytopenia (<30,000/uL)

- Uncontrolled hypertension

- Treatment with another investigational drug or device within 28 days prior to Day 1

- Prior Exposure to Sotatercept (ACE-011)

- Any serious medical condition, lab abnormality or psychiatric illness